Nonacidic multimetallic catalytic composite

ABSTRACT

A nonacidic catalytic composite especially useful for dehydrogenating dehydrogenatable hydrocarbons comprises a combination of a platinum group component, a cobalt component, a zinc component, and an alkali or alkaline earth component with a porous carrier material in amounts sufficient to result in a composite containing about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5 wt. % cobalt, about 0.01 to about 5 wt. % zinc and about 0.1 to about 5 wt. % alkali metal or alkaline earth metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of my prior, copending application Ser.No. 17,303 filed Mar. 5, 1979 and issued as U.S. Pat. No. 4,216,346 onAug. 5, 1980; which in turn is a continuation-in-part of my priorapplication Ser. No. 892,369 filed Mar. 31, 1978 and issued Dec. 18,1979 as U.S. Pat. No. 4,179,406; which in turn is a division of my priorapplication Ser. No. 744,061 filed Nov. 22, 1976 and issued Sept. 19,1978 as U.S. Pat. No. 4,115,252. All of the teachings of these priorapplications are specifically incorporated herein by reference.

The subject of the present invention is, broadly, an improved method fordehydrogenating a dehydrogenatable hydrocarbon to produce a hydrocarbonproduct containing the same number of carbon atoms but fewer hydrogenatoms. In another aspect, the present invention involves a method ofdehydrogenating normal paraffin hydrocarbons containing 4 to 30 carbonatoms per molecule to the corresponding normal mono-olefin with minimumproduction of side products. In yet another aspect, the presentinvention relates to a novel nonacidic multimetallic catalytic compositecomprising a combination of catalytically effective amounts of aplatinum group component, a cobalt component, a zinc component, and analkali or alkaline earth component with a porous carrier material. Thisnonacidic composite has highly beneficial characteristics of activity,selectivity, and stability when it is employed in the dehydrogenation ofdehydrogenatable hydrocarbons such as aliphatic hydrocarbons, naphthenehydrocarbons, and alkylaromatic hydrocarbons.

The conception of the present invention followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking function, and superior conversion,selectivity, and stability characteristics when employed in hydrocarbonconversion processes that have traditionally utilized dual-functioncatalytic composites. In my prior applications Ser. Nos. 892,369, nowU.S. Pat. No. 4,179,406, and 744,061, now U.S. Pat. No. 4,115,252, Idisclosed a significant finding with respect to a multimetalliccatalytic compsite meeting these requirements. More specifically, Idetermined that a combination of cobalt and zinc can be utilized, undercertain specified conditions, to beneficially interact with the platinumgroup component of a dual-function catalyst with a resulting markedimprovement in the performance of such a catalyst. Now I haveascertained that a catalytic composite, comprising a combination ofcatalytically effective amounts of a platinum group component, a cobaltcomponent, and a zinc component with a porous carrier material can havesuperior activity, selectivity and stability characteristics when it isemployed in a hydrocarbon dehydrogenation process if these componentsare uniformly dispersed in the porous carrier material in the amountsspecified hereinafter and if the oxidation state of the metallicingredients are carefully controlled so that substantially all of theplatinum group component is present in the elemental metallic state,substantially all of the zinc component is preferably present in apositive oxidation state, and substantially all of the catalyticallyavailable cobalt component is present in the elemental metallic state orin a state which is reducible to the elemental metallic state underhydrocarbon dehydrogenation conditions or in a mixture of these states.I have discerned, moreover, that a particularly preferred multimetalliccatalytic composite of this type contains not only a platinum groupcomponent, a cobalt component, and a zinc component, but also an alkalior alkaline earth component in an amount sufficient to ensure that theresulting catalyst is nonacidic.

The dehydrogenation of dehydrogenatable hydrocarbons is an importantcommercial process because of the great and expanding demand fordehydrogenated hydrocarbons for use in the manufacture of variouschemical products such as detergents, plastics, synthetic rubbers,pharmaceutical products, high octane gasolines, perfumes, drying oils,ion-exchange resins, and various other products well known to thoseskilled in the art. One example of this demand is in the manufacture ofhigh octane gasoline by using C₃ and C₄ mono-olefins to alkylateisobutane. Another example of this demand is in the area ofdehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins having 4 to 30 carbon atoms per molecule. These normalmono-olefins can, in turn, be utilized in the synthesis of a vast numberof other chemical products. For example, derivatives of normalmono-olefins have become of substantial importance to the detergentindustry where thay are utilized to alkylate an aromatic, such asbenzene, with subsequent transformation of the product arylalkane into awide variety of biodegradable detergents such as the alkylaryl sulfonatetypes of detergents which are most widely used today for household,industrial, and commercial purposes. Still another large class ofdetergents produced from these normal mono-olefins are the oxyalkylatedphenol derivatives in which the alkylphenol base is prepared by thealkylation of phenol with these normal mono-olefins. Still another typeof detergents produced from these normal mono-olefins are thebiodegradable alkylsulfonates formed by the direct sulfation of thenormal mono-olefins. Likewise, the olefin can be subjected to directsulfonation with sodium bisulfite to make biodegradable alkylsulfonates.As a further example, these mono-olefins can be hydrated to producealcohols which then, in turn, can be used to produce plasticizers and/orsynthetic lube oils.

Regarding the use of products made by the dehydrogenation ofalkylaromatic hydrocarbons, they find wide application in the petroleum,petrochemical, pharmaceutical, detergent, plastic, and the likeindustries. For example, ethylbenzene is dehydrogenated to producestyrene which is utilized in the manufacture of polystyrene plastics,styrene-butadiene rubber, and the like products. Isopropylbenzene isdehydrogenated to form alpha-methylstyrene which, in turn, isextensively used in polymer formation and in the manufacture of dryingoils, ion-exchange resins, and the like materials.

Responsive to this demand for these dehydrogenation products, the arthas developed a number of alternative methods to produce them incommercial quantities. One method that is widely utilized involves theselective dehydrogenation of a dehydrogenatable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst at dehydrogenationconditions. As is the case with most catalytic procedures, the principalmeasure of effectiveness for this dehydrogenation method involves theability to perform its intended function with minimum interference ofside reactions for extended periods of time. The analytical terms usedin the art to broadly measure how well a particular catalyst performsits intended functions in a particular hydrocarbon conversion reactionare activity, selectivity, and stability, and for purposes of discussionhere, these terms are generally defined for a given reactant as follows:(1) activity is a measure of the catalyst's ability to convert thehydrocarbon reactant into products at a specified severity level whereseverity level means the specific reaction conditions used--that is, thetemperature, pressure, contact time, and presence of diluents such as H₂; (2) selectivity usually refers to the amount of desired product orproducts obtained relative to the amount of the reactant charged orconverted; (3) stability refers to the rate of change with time of theactivity and selectivity parameters-- obviously the smaller rateimplying the more stable catalyst. In a dehydrogenation process, morespecifically, activity commonly refers to the amount of conversion thattakes place for a given dehydrogenatable hydrocarbon at a specifiedseverity level and is typically measured on the basis of disappearanceof the dehydrogenatable hydrocarbon; selectivity is typically measuredby the amount, calculated on a mole or weight percent of converteddehydrogenatable hydrocarbon basis, of the desired dehydrogenatedhydrocarbon obtained at the particular activity or severity level; andstability is typically equated to the rate of change with time ofactivity as measured by disappearance of the dehydrogenatablehydrocarbon and of selectivity as measured by the amount of desireddehydrogenated hydrocarbon produced. Accordingly, the major problemfacing workers in the hydrocarbon dehydrogenation art is the developmentof a more active and selective catalytic composite that has goodstability characteristics.

I have now found a multimetallic catalytic composite which possessesimproved activity, selectivity, and stability when it is employed in aprocess for the dehydrogenation of dehydrogenatable hydrocarbons. Inparticular, I have determined that the use of a multimetallic catalyst,comprising a combination of catalytically effective amounts of aplatinum group component, a cobalt component, and a zinc component witha porous refractory carrier material, can enable the performance of ahydrocarbon dehydrogenation process to be substantially improved if themetallic components are uniformly dispersed throughout the carriermaterial in the amounts stated hereinafter and if their oxidation statesare carefully controlled to be in the states hereinafter specified.Moreover, particularly good results are obtained when this composite iscombined with an amount of an alkali or alkaline earth componentsufficient to ensure that the resulting catalyst is nonacidic andutilized to produce dehydrogenated hydrocarbons containing the samecarbon structure as the reactant hydrocarbon but fewer hydrogen atoms.This nonacidic composite is particularly useful in the dehydrogenationof long chain normal paraffins to produce the corresponding normalmono-olefin with minimization of side reactions such as skeletalisomerization, aromatization, cracking and polyolefin formation. In sum,the present invention involves the significant finding that acombination of a cobalt component and a zinc component can be utilizedunder the circumstances specified herein to beneficially interact withand promote a hydrocarbon dehydrogenation catalyst containing a platinumgroup metal.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrogenation of dehydrogenatable hydrocarbonsutilizing a multimetallic catalytic composite comprising catalyticallyeffective amounts of a platinum group component, a cobalt component, anda zinc component combined with a porous carrier material. A secondobject is to provide a novel nonacidic catalytic composite havingsuperior performance characteristics when utilized in a dehydrogenationprocess. Another object is to provide an improved method for thedehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins which method minimizes undesirable side reactions such ascracking, skeletal isomerization, polyolefin formation,disproportionation and aromatization.

In brief summary, one embodiment of the present invention involves amethod for dehydrogenating a dehydrogenatable hydrocarbon whichcomprises contacting the hydrocarbon at hydrocarbon dehydrogenationconditions with a multimetallic catalytic composite comprising a porouscarrier material containing a uniform dispersion of catalyticallyeffective and available amounts of a platinum group component, a cobaltcomponent, and a zinc component. Substantially all of the platinum groupcomponent is, moreover, present in the composite in the elementalmetallic state, substantially all of the zinc component is preferablypresent in a positive oxidation state, and substantially all of thecatalytically available cobalt component is present in the correspondingelemental metallic state and/or in a state which is reducible to thecorresponding elemental metallic state under hydrocarbon dehydrogenationconditions. Further, these components are present in this composite inamounts, calculated on an elemental basis, sufficient to result in thecomposite containing about 0.01 to about 2 wt. % platinum group metal,about 0.05 to about 5 wt. % cobalt, and about 0.01 to about 5 wt. %zinc.

A second embodiment relates to the dehydrogenation method described inthe first embodiment wherein the dehydrogenatable hydrocarbon is analiphatic hydrocarbon containing 2 to 30 carbon atoms per molecule.

A third embodiment comprehends a nonacidic catalytic compositecomprising a porous carrier material having uniformly dispersed thereincatalytically effective and available amounts of a platinum groupcomponent, a cobalt component, a zinc component, and an alkali oralkaline earth component. These components are preferably present inamounts sufficient to result in the catalytic composite containing, onan elemental basis, about 0.01 to about 2 wt. % platinum group metal,about 0.1 to about 5 wt. % of the alkali metal or alkaline earth metal,about 0.05 to about 5 wt. % cobalt, and about 0.01 to about 5 wt. %zinc. In addition, substantially all of the platinum group component ispresent in the elemental metallic state, substantially all of the zinccomponent is preferably present in a positive oxidation state,substantially all of the catalytically available cobalt component ispresent in the elemental metallic state and/or in a state which isreducible to the elemental metallic state under hydrocarbondehydrogenation conditions and substantially all of the alkali oralkaline earth component is present in a positive oxidation state.

Another embodiment pertains to a method for dehydrogenating adehydrogenatable hydrocarbon which comprises contacting the hydrocarbonwith the nonacidic catalytic composite described in the third embodimentat hydrocarbon dehydrogenation conditions.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrogenatable hydrocarbons, operatingconditions for use in the dehydrogenation process, and the likeparticulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention. It is to beunderstood that (1) the term "nonacidic" means that the catalystproduces less than 10% conversion of 1-butene to isobutylene when testedat dehydrogenation conditions and, preferably, less than 1% and (2) theexpression "uniformly dispersed throughout a carrier material" isintended to mean that the amount of the subject component, expressed ona weight percent basis, is approximately the same in any reasonablydivisible portion of the carrier material as it is in gross.

Regarding the dehydrogenatable hydrocarbon that is subjected to themethod of the present invention, it can, in general, be an organiccompound having 2 to 30 carbon atoms per molecule and containing atleast one-pair of adjacent carbon atoms having hydrogen attachedthereto. That is, it is intended to include within the scope of thepresent invention, the dehydrogenation of any organic compound capableof being dehydrogenated to produce products containing the same numberof carbon atoms but fewer hydrogen atoms, and capable of being vaporizedat the dehydrogenation temperatures used herein. More particularly,suitable dehydrogenatable hydrocarbons are: aliphatic compoundscontaining 2 to 30 carbon atoms per molecule, alkylaromatic hydrocarbonswhere the alkyl group contains 2 to 6 carbon atoms, and naphthenes oralkyl-substituted naphthenes. Specific examples of suitabledehydrogenatable hydrocarbons are: (1) alkanes such as ethanes, propane,n-butane, isobutane, n-pentane, isopentane, n-hexane, 2-methylpentane,3-methylpentane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,2,2,3-trimethylbutane, and the like compounds; (2) naphthenes such ascyclopentane, cyclohexane, methylcyclopentane, ethylcyclopentane,n-propylcyclopentane, 1,3-dimethylcyclohexane, and the like compounds;and (3) alkylaromatics such as ethylbenzene, n-butylbenzene,1,3,5-triethylbenzene, isopropylbenzene, isobutylbenzene,ethylnaphthaline, and the like compounds.

In a preferred embodiment, the dehydrogenatable hydrocarbon is a normalparaffin hydrocarbon having about 3 to 30 carbon atoms per molecule. Forexample, normal paraffin hydrocarbons containing about 10 to 18 carbonatoms per molecule are dehydrogenated by the subject method to producethe corresponding normal mono-olefin which can, in turn, be alkylatedwith benzene and sulfonated to make alkylbenzene sulfonate detergentshaving superior biodegradability. Likewise, n-alkanes having 10 to 18carbon atoms per molecule can be dehydrogenated to the correspondingnormal mono-olefin which, in turn, can be sulfonated or sulfated to makeexcellent detergents. Similarly, n-alkanes having 6 to 10 carbon atomscan be dehydrogenated to form the corresponding mono-olefin which can,in turn, be hydrated to produce valuable alcohols. Preferred feed steamsfor the manufacture of detergent intermediates contain a mixture of 4 or5 adjacent normal paraffin homologues such as C₁₀ to C₁₃, C₁₁ to C₁₄,C₁₁ to C₁₅ and the like mixtures.

The multimetallic catalyst used in the present invention comprises aporous carrier material or support having combined therewith a uniformdispersion of catalytically effective amounts of a platinum groupcomponent, a cobalt component, a zinc component and, in the preferredcase, an alkali or alkaline earth component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high-surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the dehydrogenation process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts, such as: (1) activated carbon, coke,charcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated, for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria, boria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels suzn as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, MnAl.sub. 2 O₄, CaAl₂ O₄ and other like compounds havingthe formula MO.Al₂ O₃ where M is a metal having a valence of 2; and (7)combinations of elements from one or more of these groups. The preferredporous carrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas the gamma-, eta-, and theta-alumina, with gamma-, or eta-aluminagiving best results. In addition, in some embodiments the aluminacarrier material may contain miner proportions of other well-knownrefractory inorganic oxides such as silica, zirconia, magnesia, etc.;however, the preferred support is substantially pure gamma- oreta-alumina. Preferred carrier materials have an apparent bulk densityof about 0.2 to about 0.7 g/cc and surface area characteristics suchthat the average pore diameter is about 20 to about 300 Angstroms, thepore volume (B.E.T.) is about 0.1 to about 1 cc/g and the surface area(B.E.T.) is about 100 to about 500 m² /g. In general, best results aretypically obtained with a gamma-alumina carrier material which is usedin the form of spherical particles having: a relatively small diameter(i.e. typically about 1/16 inch), an apparent bulk density of about 0.2to about 0.6 (most preferably about 0.3) g/cc, a pore volume (B.E.T.) ofabout 0.4 cc/g, and a surface area (B.E.T.) of about 100 to about 250 m²/g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, etc., and utilized in any desiredsize. For the purpose of the present invention, a particularly preferredform of alumina is the sphere; and alumina spheres may be continuouslymanufactured by the well-known oil drop method which comprises: formingan alumina hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid, combiningthe resulting hydrosol with a suitable gelling agent and dropping theresultant mixture into an oil bath maintained at elevated temperatures.The droplets of the mixture remain in the oil bath until they set andform hydrogel spheres. The spheres are then continuously withdrawn fromthe oil bath and typically subjected to specific aging treatments in oiland an ammoniacal solution to further improve their physicalcharacteristics. The resulting aged and gelled particles are then washedand dried at a relatively low temperature of about 300° F. to about 400°F. and subjected to a calcination procedure at a temperature of about850° F. to about 1300° F. for a period of about 1 to about 20 hours. Itis a good practice to subject the calcined particles to a hightemperature treatment with steam in order to remove undesired acidiccomponents such as residual chloride. This procedure effects conversionof the alumina hydrogel to the corresponding crystalline gamma-alumina.See the teachings of U.S. Pat. No. 2,620,314 for additional details.

The expression "catalytically available cobalt" as used herein isintended to mean the portion of the cobalt component that is availablefor use in accelerating the dehydrogenation reaction of interest. Forcertain types of carrier materials which can be used in the preparationof the instant catalyst composite, it has been observed that a portionof the cobalt incorporated therein is essentially bound-up in thecrystal structure thereof in a manner which essentially makes itcatalytically unavailable; in fact it is more a part of the refractorycarrier material than a catalytically active component. Specificexamples of this effect are observed when the carrier material can forma spinel or spinel-like structure with a portion of the cobalt componentand/or when a refractory cobalt oxide or aluminate is formed by reactionof the carrier material (or precursor thereof) with a portion of thecobalt component. When this effect occurs, it is only with greatdifficulty that the portion of the cobalt bound-up with the support canbe reduced to a catalytically active state and the conditions requiredto do this are beyond the severity levels normally associated withdehydrogenation conditions and are in fact likely to seriously damagethe necessary porous characteristics of the support. In the cases wherecobalt can interact with the crystal structure of the support to rendera portion thereof catalytically unavailable, the concept of the presentinvention merely requires that the amount of cobalt added to the subjectcatalyst be adjusted to satisfy the requirements of the support as wellas the catalytically available cobalt requirements of the presentinvention. Against this background then, the hereinafter statedspecifications for oxidation state and dispersion of the cobaltcomponent are to be interpreted as directed to a description of thecatalytically available cobalt. On the other hand, the specificationsfor the amount of cobalt used are to be interpreted to include all ofthe cobalt contained in the catalyst in any form.

One essential constituent of the multimetallic catalyst of the presentinvention is a zinc component. This component may in general be presentin the instant catalytic composite in any catalytically available formsuch as the elemental metal, a compound like the oxide, hydroxide,halide, oxyhalide, aluminate, or in chemical combination with one ormore of the other ingredients of the catalyst. Although it is notintended to restrict the present invention by this explanation it isbelieved that best results are obtained when the zinc component ispresent in the composite in a form wherein substantially all of the zincmoiety is in an oxidation state above that of the elemental metal suchas in the form of zinc oxide or zinc aluminate, or a mixture thereof,and the subsequently described oxidation and reduction steps that arepreferably used in the preparation of the instant catalytic compositeare specifically designed to achieve this end. The term "zinc aluminate"as used herein refers to a coordinated complex of zinc, oxygen, andaluminum which are not necessarily present in the same relationship forall cases covered herein. This zinc component can be used in any amountwhich is catalytically effective, with good results obtained, on anelemental basis, with about 0.01 to about 5 wt. % zinc in the catalyst.Best results are ordinarily achieved with about 0.05 to about 1 wt. %zinc, calculated on an elemental basis.

This zinc component may be incorporated into the catalytic composite inany suitable manner known to the art to result in a relatively uniformdispersion of the zinc moiety in the carrier material, such as bycoprecipitation or cogellation or coextrusion with the porous carriermaterial, ion exchange with the gelled carrier material, or impregnationwith the carrier material either after, before, or during the periodwhen it is dried and calcined. It is to be noted that it is intended toinclude within the scope of the present invention all conventionalmethods for incorporating and simultaneously uniformly distributing ametallic component in a catalytic composite and the particular method ofincorporation used is not deemed to be an essential feature of thepresent invention. One especially preferred method of incorporating thezinc component into the catalytic composite involves cogelling orcorprecipitating or coextruding the zinc component in the form of thecorresponding hydrous oxide during the preparation of the preferredcarrier material, alumina. This method typically involves the additionof a suitable sol-soluble zinc compound such as zinc nitrate to thealumina hydrosol and then combining the hydrosol with a suitable gellingagent and dropping the resulting mixture into an oil bath, etc., asexplained in detail hereinbefore. Alternatively, the zinc compound canbe added to the gelling agent. After drying and calcining the resultinggelled carrier material in air, there is obtained an intimatecombination of alumina and zinc oxide and/or aluminate. Anotherpreferred method of incorporating the zinc component into the catalyticcomposite involves utilization of a soluble, decomposable compound ofzinc to impregnate the porous carrier material. In general, the solventused in this impregnation step is selected on the basis of thecapability to dissolve the desired zinc compound without adverselyaffecting the carrier material or the other ingredients of thecatalyst--for example, a suitable alcohol, ether, acid and the likesolvents. The solvent is preferably an aqueous, acidic solution. Thus,the zinc component may be added to the carrier material by comminglingthe latter with an aqueous acidic solution of suitable zinc salt,complex, or compound such as zinc acetate, ammonium tetrachlorozincate,zinc borate, zinc bromate, zinc bromide, zinc carbonate, zincperchlorate, zinc chloride, zinc chloroplatinate, zinc fluoride, zincformate, zinc hydroxide, zinc nitrate, zinc oxide, any of the solublezincate salts, and the like compounds. A particularly preferredimpregnation solution comprises an acidic aqueous solution of zincnitrate. Suitable acids for use in the impregnation solution are:inorganic acids such as hydrochloric acid, nitric acid, and the like,and strongly acidic organic acids such as oxalic acid, malonic acid,citric acid, and the like. In general, the zinc compound can beimpregnated either prior to, simultaneously with, or after the otheringredients are added to the carrier material. However, excellentresults are obtained when the zinc component is added to the carriermaterial prior to or simultaneously with the addition of the platinumgroup component. In fact, a preferred preparation procedure involves atwo step impregnation procedure wherein the first impregnation step usesan aqueous acidic impregnation solution containing chloroplatinic acid,zinc nitrate and nitric acid.

A second essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as asecond component of the present composite. It is an essential feature ofthe present invention that substantially all of this platinum groupcomponent exists within the final catalytic composite in the elementalmetallic state. Generally, the amount of this component present in thefinal catalytic composite is small compared to the quantities of theother components combined therewith. In fact, the platinum groupcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum, iridium, rhodium, or palladium metal. Particularlypreferred mixtures of these metals are platinum and iridium and platinumand rhodium.

This platinum group component may be incorporated in the catalyticcomposite in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion-exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium dioxide, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium chloroiridate, potassium rhodiumoxalate, etc. The utilization of a platinum, iridium, rhodium, orpalladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is ordinarilypreferred. Hydrogen chloride, nitric acid, or the like acid is alsogenerally added to the impregnation solution in order to furtherfacilitate the uniform distribution of the metallic componentsthroughout the carrier material. In addition, it is generally preferredto impregnate the carrier material after it has been calcined in orderto minimize the risk of washing away the valuable platinum or palladiumcompounds; however, in some cases it may be advantageous to impregnatethe carrier material when it is in a gelled state.

A third essential ingredient of the instant multimetallic catalyticcomposite is a cobalt component. Although this component may beinitially incorporated into the composite in many different decomposableforms which are hereinafter stated, my basic finding is that thecatalytically active state for hydrocarbon conversion with thiscomponent is the elemental metallic state. Consequently, it is a featureof this invention that substantially all of the catalytically availablecobalt component exists in the catalytic composite either in theelemental metallic state or in a state which is reducible to theelemental state under hydrocarbon dehydrogenation conditions or in amixture of these states. Examples of this last state are obtained whenthe catalytically available cobalt component is initially present in theform of cobalt oxide, hydroxide, halide, oxyhalide, and the likereducible compounds. As a corollary to this basic finding on the activestate of the catalytically available cobalt component, it follows thatthe presence of the catalytically available cobalt in forms which arenot reducible at hydrocarbon dehydrogenation conditions is to bescrupulously avoided if the full benefits of the present invention areto be realized. Illustrative of these undesired forms are cobalt sulfideand the cobalt oxysulfur compounds such as cobalt sulfate. Best resultsare obtained when the composite initially contains all of thecatalytically available cobalt component in the elemental metallic stateor in a reducible oxide state or in a mixture of these states. Allavailable evidence indicates that the preferred preparation procedurespecifically described in Example I results in a catalyst having thecatalytically available cobalt component present in the form of amixture of the reducible oxide and the elemental metal. Based on theperformance of such a catalyst, it is believed that substantially all ofthis reducible oxide form of the cobalt component is reduced to theelemental metallic state when a dehydrogenation process using thiscatalyst is started-up and lined-out at hydrocarbon dehydrogenationconditions. The cobalt component may be utilized in the composite in anyamount which is catalytically effective, with the preferred amount beingabout 0.05 to about 5 wt. % thereof, calculated on an elemental cobaltbasis. Typically, best results are obtained with about 0.1 to about 2.5wt. % cobalt. It is, additionally, preferred to select the specificamount of cobalt from within this broad weight range as a function ofthe amount of the platinum group component, on an atomic basis, as isexplained hereinafter.

The cobalt component may be incorporated into the catalytic composite inany suitable manner known to those skilled in the catalyst formulationart to result in a relatively uniform distribution of the catalyticallyavailable cobalt in the carrier material such as coprecipitation,cogelation, ion-exchange, impregnation, etc. In addition, it may beadded at any stage of the preparation of the composite--either duringpreparation of the carrier material or thereafter--since the precisemethod of incorporation used is not deemed to be critical. However, bestresults are obtained when the catalytically available cobalt componentis relatively uniformly distributed throughout the carrier material in arelatively small particle or crystallite size having a maximum dimensionof less than 100 Angstroms, and the preferred procedures are the onesthat are known to result in a composite having a relatively uniformdistribution of the catalytically available cobalt moiety in arelatively small particle size. One acceptable procedure forincorporating this component into the composite involves cogelling orcoprecipitating the cobalt component during the preparation of thepreferred carrier material, alumina. This procedure usually comprehendsthe addition of a soluble, decomposable, and reducible compound ofcobalt such as cobalt acetate or chloride or nitrate to the aluminahydrosol before it is gelled. Alternatively, the reducible compound ofcobalt can be added to the gelling agent before it is added to thehydrosol. The resulting mixture is then finished by conventionalgelling, aging, drying, and calcination steps as explained hereinbefore.One preferred way of incorporating this component is an impregnationstep wherein the porous carrier material is impregnated with a suitablecobalt-containing solution either before, during, or after the carriermaterial is calcined or oxidized. The solvent used to form theimpregnation solution may be water, alcohol, ether, or any othersuitable organic or inorganic solvent provided the solvent does notadversely interact with any of the other ingredients of the composite orinterfere with the distribution and reduction of the cobalt component.Preferred impregnation solutions are aqueous solutions of water-soluble,decomposable, and reducible cobalt compounds such as cobaltous acetate,cobaltous benzoate, cobaltous bromate, cobaltouse bromide, cobaltouschlorate and perchlorate, cobaltous chloride, cobaltic chloride,cobaltous fluoride, cobaltous iodide, cobaltous nitrate, hexamminecobalt(III) chloride, hexamminecobalt (III) nitrate, triethylenediamminecobalt(III) chloride, cobaltous hexamethylenetetramine, and the likecompounds. Best results are ordinarily obtained when the impregnationsolution is an aqueous solution of cobalt acetate or cobalt nitrate.This cobalt component can be added to the carrier material, either priorto, simultaneously with, or after the other metallic components arecombined therewith. Best results are usually achieved when thiscomponent is added after the platinum group and zinc components havebeen impregnated via an aqueous impregnation solution. In fact,excellent results are obtained, as reported in the examples, with a twostep impregnation procedure using a second aqueous acidic impregnationsolution containing cobalt acetate or nitrate and nitric acid.

A highly preferred ingredient of the catalyst used in the presentinvention is the alkali or alkaline earth component. More specifically,this component is selected from the group consisting of the compounds ofthe alkali metals--cesium, rubidium, potassium, sodium, and lithium--andof the alkaline earth metals--calcium, strontium, barium, and magnesium.This component exists within the catalytic composite in an oxidationstate above that of the elemental metal such as a relatively stablecompound such as the oxide or hydroxide, or in combination with one ormore of the other components of the composite, or in combination withthe carrier material such as, for example, in the form of an alkali oralkaline earth metal aluminate. Since, as is explained hereinafter, thecomposite containing the alkali or alkaline earth component is alwayscalcined or oxidized in an air atmosphere before use in thedehydrogenation of hydrocarbons, the most likely state this componentexists in during use in the dehydrogenation reaction is thecorresponding metallic oxide such as lithium oxide, potassium oxide,sodium oxide, and the like. Regardless of what precise form in which itexists in the composite, the amount of this component utilized ispreferably selected to provide a nonacidic composite containing about0.1 to about 5 wt. % of the alkali metal or alkaline earth metal, and,more preferably, about 0.25 to about 3.5 wt. %. Best results areobtained when this component is a compound of lithium or potassium. Thefunction of this component is to neutralize any of the acidic materialsuch as halogen which may have been used in the preparation of thepresent catalyst so that the final catalyst is nonacidic.

This alkali or alkaline earth component may be combined with the porouscarrier material in any manner known to those skilled in the art toresult in a relatively uniform dispersion of this component throughoutthe carrier material with consequential neutralization of any acidicsites which may be present therein. Typically good results are obtainedwhen it is combined by impregnation, coprecipitation, ion-exchange, andthe like procedures. The preferred procedure, however, involvesimpregnation of the carrier material either before, during, or after itis calcined, or before, during, or after the other metallic ingredientsare added to the carrier material. Best results are ordinarily obtainedwhen this component is added to the carrier material after the platinumgroup and zinc components because the alkali metal or alkaline earthmetal component acts to neutralize the acidic materials used in thepreferred impregnation procedure for these metallic components. In fact,it is preferred to add the platinum group and zinc components to thecarrier material, oxidize the resulting composite in a wet air stream ata high temperature (i.e. typically about 600° to 1000° F.), then treatthe resulting oxidized composite with steam or a mixture of air andsteam at a relatively high temperature of about 800° to about 1050° F.in order to remove at least a portion of any residual activity andthereafter add the cobalt and the alkali metal or alkaline earthcomponents. Typically, the impregnation of the carrier material withthis component is performed by contacting the carrier material with asolution of a suitable decomposable compound or salt of the desiredalkali or alkaline earth metal. Hence, suitable compounds include thealkali metal or alkaline earth metal halides, nitrates, acetates,carbonates, phosphates, and the like compounds. For example, excellentresults are obtained by impregnating the carrier material after theplatinum group and zinc components have been combined therewith, with anaqueous solution of lithium nitrate or potassium nitrate and cobaltacetate or nitrate.

Regarding the preferred amounts of the metallic components of thesubject catalyst, I have found it to be a beneficial practice to specifythe amounts of these metallic components not only on an absolute basisbut also as a function of the amount of the platinum group component,expressed on an atomic basis. Quantitatively, the amount of the cobaltcomponent is preferably sufficient to provide an atomic ratio of cobaltto platinum group metal of about 0.1:1 to about 66:1, with best resultsobtained at an atomic ratio of about 0.4:1 to about 18:1. Similarly, itis a good practice to specify the amount of the zinc component so thatthe atomic ratio of zinc to platinum group metal contained in thecomposite is about 0.1:1 to about 10:1, with the preferred range beingabout 0.5:1 to about 5:1. In the same manner, the amount of the alkalior alkaline earth component is ordinarily selected to produce acomposite having an atomic ratio of alkali metal or alkaline earth metalto platinum group metal of about 5:1 to about 100:1 or more, with thepreferred range being about 10:1 to about 75:1.

Another significant parameter for the instant nonacidic catalyst is the"total metals content" which is defined to be the sum of the platinumgroup component, the cobalt component, the zinc component, and thealkali or alkaline earth component, calculated on an elemental metalbasis. Good results are ordinarily obtained with the subject catalystwhen this parameter is fixed at a value of about 0.2 to about 5 wt. %,with best results ordinarily achieved at a metals loading of about 0.4to about 4 wt. %.

Integrating the above discussion of each of the essential and preferredcomponents of the catalytic composite used in the present invention, itis evident that an especially preferred nonacidic catalytic compositecomprises a combination of a platinum group component, a cobaltcomponent, a zinc component, and an alkali or alkaline earth componentwith an alumina carrier material in amounts sufficient to result in thecomposite containing from about 0.05 to about 1 wt. % platinum groupmetal, about 0.1 to about 2.5 wt. % cobalt, about 0.25 to about 3.5 wt.% alkali metal or alkaline earth metal, and about 0.05 to about 1 wt. %zinc.

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the resulting multimetalliccomposite generally will be dried at a temperature of about 200° F. toabout 600° F. for a period of from about 2 to about 24 hours or more,and finally calcined or oxidized at a temperature of about 600° F. toabout 1100° F. (preferably about 800° to about 950° F.) in an airatmosphere for a period of about 0.5 to 10 hours, preferably about 1 toabout 5 hours, in order to convert substantially all the metalliccomponents to the corresponding oxide form. When acidic components arepresent in any of the reagents used to effect incorporation of any oneof the components of the subject composite, it is a good practice tosubject the resulting composite to a high temperature treatment withsteam or with a mixture of steam and air, either before, during or afterthis oxidation step in order to remove as much as possible of theundesired acidic component. For example, when the platinum groupcomponent is incorporated by impregnating the carrier material withchloroplatinic acid, it is preferred to subject the resulting compositeto a high temperature treatment with steam or a mixture of steam and airat a temperature of about 600° to 1100° F. in order to remove as much aspossible of the undesired chloride.

The resultant oxidized catalytic composite is preferably subjected to asubstantially water-free reduction step prior to its use in thedehydrogenation of hydrocarbons. This step is designed to selectivelyreduce the platinum group component to the corresponding metal, whilepreferably maintaining the zinc component in a positive oxidation stateand to insure a uniform and finely divided dispersion of the metalliccomponents throughout the carrier material. It is a good practice to drythe oxidized catalyst prior to this reduction step by passing a streamof dry air or nitrogen through same at a temperature of about 500° to1100° F. (preferably about 800° to about 950° F.) and at a GHSV of about100 to 800 hr.⁻¹ until the effluent stream contains less than 1000 ppm.of H₂ O and preferably less than 500 ppm. Preferably, a substantiallypure and dry hydrogen stream (i.e. less than 20 vol. ppm. H₂ O) is usedas the reducing agent in this reduction step. The reducing agent iscontacted with the oxidized catalyst at conditions including atemperature of about 600° F. to about 1200° F. (preferably about 800° toabout 1000° F.), a GHSV of about 300 to 1000 hr.⁻¹, and a period of timeof about 0.5 to 10 hours effective to reduce substantially all of theplatinum group component to the elemental metallic state, whilepreferably maintaining the zinc component in an oxidation state abovethat of the elemental metal. This reduction treatment may be performedin situ as part of a start-up sequence if precautions are taken topredry the plant to a substantially water-free state and if asubstantially water-free hydrogen stream is used.

Although using the subject catalyst in a substantially sulfur-free stateis an especially preferred mode of operation for the present hydrocarbondehydrogenation method (as explained in the teachings of my priorapplications Ser. Nos. 892,369 and 744,061, the resulting selectivelyreduced catalytic composite may in some circumstances be beneficiallysubjected to a presulfiding operation designed to incorporate in thecatalytic composite from about 0.01 to about 0.5 wt. % sulfur,calculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitablesulfur-containing sulfiding reagent such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the selectively reduced catalyst with asulfiding reagent such as a mixture of hydrogen and hydrogen sulfidehaving about 10 moles of hydrogen per mole of hydroxy sulfide atconditions sufficient to effect the desired incorporation of sulfur,generally including a temperature ranging from about 50° F. up to about1100° F. or more. It is generally a good practice to perform thispresulfiding step under substantially water-free conditions. Althoughnot preferred, it is within the scope of the present invention tomaintain or achieve the sulfided state of the instant catalyst duringuse in the dehydrogenation of hydrocarbons by continuously orperiodically adding a decomposable sulfur-containing compound, such asthe sulfiding reagents previously mentioned, to the reactor containingthe catalyst in an amount sufficient to provide about 1 to 500 wt. ppm.,preferably 1 to 20 wt. ppm. of sulfur based on hydrocarbon charge.

According to the method of the present invention, the dehydrogenatablehydrocarbon is contacted with the multimetallic catalytic compositedescribed above in a dehydrogenation zone maintained at dehydrogenationconditions. This contacting may be accomplished by using the catalyst ina fixed bed system, a moving bed system, a fluidized bed system, or in abatch type operation; however, in view of the danger of attrition lossesof the valuable catalyst and of well-known operational advantages, it ispreferred to use a fixed bed system. In this system, the hydrocarbonfeed stream is preheated by any suitable heating means to the desiredreaction temperature and then passed into a dehydrogenation zonecontaining a fixed bed of the catalyst previously characterized. It is,of course, understood that the dehydrogenation zone may be one or moreseparate reactors with suitable heating means therebetween to insurethat the desired conversion temperature is maintained at the entrance toeach reactor. It is also to be noted that the reactants may be contactedwith the catalyst bed in either upward, downward, or radial flow fashionwith the latter being preferred. In addition, it is to be noted that thereactants may be in the liquid phase, a mixed liquid-vapor phase, or avapor phase when the contact the catalyst, with best results obtained inthe vapor phase.

Although hydrogen is the preferred diluent for use in the subjectdehydrogenation method, in some cases other art-recognized diluents maybe advantageously utilized, either individually or in admixture withhydrogen or each other, such as steam, methane, ethane, carbon dioxide,and the like diluents. Hydrogen is preferred because it serves thedual-function of not only lowering the partial pressure of thedehydrogenatable hydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits on the catalytic composite.Ordinarily, hydrogen is utilized in amounts sufficient to insure ahydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1, with bestresults obtained in the range of about 1.5:1 to about 10:1. The hydrogenstream charged to the dehydrogenation zone will typically be recycledhydrogen obtained from the effluent stream from this zone after asuitable hydrogen separation step. As is explained in my priorapplications Ser. Nos. 892,369 and 744,061, a highly preferred mode ofoperation of the instant dehydrogenation method is in a substantiallywater-free environment; however, when utilizing hydrogen in the instantmethod, improved selectivity results are obtained under certain limitedcircumstances, if water or a water-producing substance (such as analcohol, ketone, ether, aldehyde, or the like oxygen-containingdecomposable organic compound) is added to the dehydrogenation zone inan amount calculated on the basis of equivalent water, corresponding toabout 1 to about 5,000 wt. ppm. of the hydrocarbon charge stock, withabout 1 to 1,000 wt. ppm. of water giving best results. This wateraddition feature may be used on a continuous or intermittent basis toregulate the activity and selectivity of the instant catalyst.

Regarding the conditions utilized in the method of the presentinvention, these are generally selected from the dehydrogenationconditions well known to those skilled in the art for the particulardehydrogenatable hydrocarbon which is charged to the process. Morespecifically, suitable conversion temperatures are selected from therange of about 700° to about 1200° F. with a value being selected fromthe lower portion of this range for the more easily dehydrogenatedhydrocarbons such as the long chain normal paraffins and from the higherportion of this range for the more difficultly dehydrogenatedhydrocarbons such as propane, butane, and the like hydrocarbons. Forexample, for the hydrogenation of C₆ to C₃₀ normal paraffins, bestresults are ordinarily obtained at a temperature of about 800° to about950° F. The pressure utilized is ordinarily selected at a value which isas low as possible consistent with the maintenance of catalyst stabilityand is usually about 0.1 to about 10 atmospheres with best resultsordinarily obtained in the range of about 0.5 to about 3 atmospheres. Inaddition, a liquid hourly space velocity (calculated on the basis of thevolume amount, as a liquid, of hydrocarbon charged to thedehydrogenation zone per hour divided by the volume of the catalyst bedutilized) is selected from the range of about 1 to about 40 hr.⁻¹, withbest results for the dehydrogenation of long chain normal paraffinstypically obtained at a relatively high space velocity of about 25 to 35hr.⁻¹.

Regardless of the details concerning the operation of thedehydrogenation step, an effluent stream will be withdrawn therefrom.This effluent will usually contain unconverted dehydrogenatablehydrocarbons, hydrogen, and products of the dehydrogenation reaction.This stream is typically cooled and passed to a hydrogen-separating zonewherein a hydrogen-rich vapor phase is allowed to separate from ahydrogen-rich liquid phase. In general, it is usually desired to recoverthe unreacted dehydrogenatable hydrocarbon from this hydrocarbon-richliquid phase in order to make the dehydrogenation process economicallyattractive. This recovery operation can be accomplished in any suitablemanner known to the art such as by passing the hydrocarbon-rich liquidphase through a bed of suitable adsorbent material which has thecapability to selectively retain the dehydrogenated hydrocarbonscontained therein or by contacting same with a solvent having a highselectivity for the dehydrogenated hydrocarbon, or by a suitablefractionation scheme where feasible. In the case where thedehydrogenated hydrocarbon is a mono-olefin, suitable adsorbents havingthis capability are activated silica gel, activated carbon, activatedalumina, various types of specially prepared zeolitic crystallinealuminosilicates, molecular sieves, and the like adsorbents. In anothertypical case, the dehydrogenated hydrocarbons can be separated from theunconverted dehydrogenatable hydrocarbons by utilizing the inherentcapability of the dehydrogenated hydrocarbons to easily enter intoseveral well-known chemical reactions such as alkylation,oligomerization, halogenation, sulfonation, hydration, oxidation, andthe like reactions. Irrespective of how the dehydrogenated hydrocarbonsare separated from the unreacted hydrocarbons, a stream containing theunreacted dehydrogenatable hydrocarbons will typically be recovered fromthis hydrocarbon separation step and recycled to the dehydrogenationstep. Likewise, the hydrogen phase present in the hydrogen-separatingzone will be withdrawn therefrom, a portion of it vented from the systemin order to remove the net hydrogen make, and the remaining portion istypically recycled through suitable compressing means to thedehydrogenation step in order to provide diluent hydrogen therefor.

In a preferred embodiment of the present invention wherein long chainnormal paraffin hydrocarbons are dehydrogenated to the correspondingnormal mono-olefins, a preferred mode of operation of this hydrocarbonrecovery step involves an alkylation reaction. In this mode, thehydrocarbon-rich liquid phase withdrawn from the hydrogen-separatingzone is combined with a stream containing an alkylatable aromatic andthe resulting mixture passed to an alkylation zone containing a suitablehighly acid catalyst such as an anhydrous solution of hydrogen fluoride.In the alkylation zone the mono-olefins react with alkylatable aromaticwhile the unconverted normal paraffins remain substantially unchanged.The effluent stream from the alkylation zone can then be easilyseparated, typically by means of a suitable fractionation system, toallow recovery of the unreacted normal paraffins. The resulting streamof unconverted normal paraffins is then usually recycled to thedehydrogenation step of the present invention.

The following working examples are introduced to illustrate further thedehydrogenation method and nonacidic multimetallic catalytic compositeof the present invention. These examples of specific embodiments of thepresent invention are intended to be illustrative rather thanrestrictive.

These examples are all performed in a laboratory scale dehydrogenationplant comprising a reactor, a hydrogen separating zone, heating means,cooling means, pumping means, compressing means, and the likeconventional equipment. In this plant, the feed stream containing thedehydrogenatable hydrocarbon is combined with a hydrogen-containingrecycle gas stream containing water in an amount corresponding to about100 wt. ppm.. of the hydrocarbon feed and the resultant mixture heatedto the desired conversion temperature, which refers herein to thetemperature maintained at the inlet to the reactor. The heated mixtureis then passed into contact with the instant multimetallic catalystwhich is maintained as a fixed bed of catalyst particles in the reactor.The pressures reported herein are recorded at the outlet from thereactor. An effluent stream is withdrawn from the reactor, cooled, andpassed into the hydrogen-separating zone wherein a hydrogen-containinggas phase separates from a hydrocarbon-rich liquid phase containingdehydrogenated hydrocarbons, unconverted dehydrogenatable hydrocarbons,and a minor amount of side products of the dehydrogenation reaction. Aportion of the hydrogen-containing gas phase is recovered as excessrecycle gas with the remaining portion being continuously recycled,after water addition as needed, through suitable compressing means tothe heating zone as described above. The hydrocarbon-rich liquid phasefrom the separating zone is withdrawn therefrom and subjected toanalysis to determine conversion and selectivity for the desireddehydrogenated hydrocarbon as will be indicated in the Examples.Conversion number of the dehydrogenatable hydrocarbon reported hereinare all calculated on the basis of disappearance of the dehydrogenatablehydrocarbon and are expressed in mole percent. Similarly, selectivitynumbers are reported on the bases of moles of desired hydrocarbonproduced per 100 moles of dehydrogenatable hydrocarbon converted.

All of the catalysts utilized in these examples are prepared accordingto the following preferred method with suitable modification instoichiometry to achieve the compositions reported in each example.First, an alumina carrier material comprising 1/16 inch spheres havingan apparent bulk density of about 0.3 g/cc is prepared by: forming analumina hydroxyl chloride sol by dissolving substantially pure aluminumpellets in a hydrochloric acid solution, adding hexamethylenetetramineto the resulting alumina sol, gelling the resulting solution by droppingit into an oil bath to form spherical particles of an alumina hydrogel,aging, and washing the resulting particles with an ammoniacal solutionand finally drying, calcining, and steaming the aged and washedparticles to form spherical particles of gamma-alumina containingsubstantially less than 0.1 wt. % combined chloride. Additional detailsas to this method of preparing this alumina carrier material are givenin the teachings of U.S. Pat. No. 2,620,314.

The resulting gamma-alumina particles are then contacted in a firstimpregnation step at suitable impregnation conditions with a firstaqueous impregnation solution containing chloroplatinic acid, zincnitrate and nitric acid in amounts sufficient to yield a finalmultimetallic catalytic composite containing a uniform dispersion of thehereinafter specified amounts of platinum and zinc. The nitric acid isutilized in an amount of about 5 wt. % of the alumina particles. Inorder to ensure a uniform dispersion of the metallic components in thecarrier material, the impregnation solution is maintained in contactwith the carrier material particles for about 1/2 hour at a temperatureof about 70° F. with constant agitation. The impregnated spheres arethen dried at a temperature of about 225° F. for about an hour andthereafter calcined or oxidized in an air atmosphere containing about 5to 25 vol. % H₂ O at a temperature of about 500° F. to about 1000° F.(preferably about 800° to 950° F.) for about 2 to 10 hours effective toconvert all of the metallic components to the corresponding oxide forms.In general, it is a good practice to thereafter treat the resultingoxidized particles with an air stream containing about 10 to about 30%steam at a temperature of about 800° F. to about 1000° F. for anadditional period of about 1 to about 5 hours in order to reduce anyresidual combined chloride contained in the catalyst to a value of lessthan 0.5 wt. % and preferably less than 0.2 wt. %.

The cobalt component is thereafter added to this oxidized andsteam-stripped catalyst in a second impregnation step. In the casesshown in the examples where the catalyst utilized contains an alkali oralkaline earth component, this component is also added to the oxidizedand steam-treated multimetallic catalyst in this second impregnationstep. This second impregnation step involves contacting the oxidized andsteamed multimetallic catalyst with an aqueous acidic solution of asuitable soluble and decomposable salt of cobalt and of the alkali oralkaline earth component (when it is to be added) under conditionsselected to result in a uniform dispersion of these components in thecarrier material. For the catalysts utilized in the present examples,the salts are cobalt nitrate or acetate and either lithium nitrate orpotassium nitrate. The amounts of the salts of cobalt and of the alkalimetal utilized are chosen to result in a final catalyst containing therequired amount of cobalt and having the desired nonacidiccharacteristics. The resulting cobalt and alkali or alkalineearth-impregnated particles are then preferably dried and oxidized in anair atmosphere in much the same manner as is described above followingthe first impregnation step. In some cases, it is possible to combineboth of these impregnation steps into a single step, therebysignificantly reducing the time and complexity of the catalystmanufacturing procedure.

The resulting oxidized catalyst is thereafter subjected to a drying stepwhich involves contacting the oxidized particles with a dry air streamat a temperature of about 930° C., a GHSV of 300 hr.⁻¹ for a period ofabout 10 hours. The dried catalyst is then purged with a dry nitrogenstream and thereafter selectively reduced by contacting with a dryhydrogen stream at conditions including a temperature of about 870° F.,atmospheric pressure and a gas hourly space velocity of about 500 hr.⁻¹,for a period of about 1 to 10 hours effective to at least reducesubstantially all of the platinum group component to the correspondingelemental metal, while maintaining the alkali or alkaline earth and zinccomponents in a positive oxidation state.

EXAMPLE I

The reactor is loaded with 100 cc of a catalyst containing, on anelemental basis, 0.3 wt. % platinum, 1.0 wt. % cobalt and 0.25 wt. %zinc, and less than 0.15 wt. % chloride. This corresponds to an atomicratio of zinc to platinum of 2.5:1 and of cobalt to platinum of 11:1.The feed stream utilized is commercial grade isobutane containing 99.7wt. % isobutane and 0.3 wt. % normal butane. The feed stream iscontacted with the catalyst at a temperature of 1020° F., a pressure of10 psig., a liquid hourly space velocity of 4.0 hr.⁻¹, and a recycle gasto hydrocarbon mole ratio of 3:1. The dehydrogenation plant is lined-outat these conditions and a 20 hour test period commenced. The hydrocarbonproduct stream from the plant is continuously analyzed by GLC (gasliquid chromatography) and a high conversion of isobutane is observedwith a high selectivity for isobutylene.

EXAMPLE II

The catalyst contains, on an elemental basis, 0.375 wt. % platinum, 0.5wt. % cobalt, 0.2 wt. % zinc, 0.6 wt. % lithium, and 0.15 wt. % combinedchloride. These amounts correspond to the following atomic ratios: (1)Zn/pt of 1.6:1, (2) Co/Pt of 4.4:1, and (3) Li/Pt of 45:1. The feedstream is commercial grade normal dodecane. The dehydrogenation reactoris operated at a temperature of 850° F., a pressure of 10 psig., aliquid hourly space velocity of 32 hr.⁻¹, and a recycle gas tohydrocarbon mole ratio of 5:1. After a line-out period, a 20 hour testperiod is performed during which the average conversion of the normaldodecane is maintained at a high level with a selectivity for normaldodecane of about 90%.

EXAMPLE III

The catalyst is the same as utilized in Example II. The feed stream isnormal tetradecane. The conditions utilized are a temperature of 830°F., a pressure of 20 psig., a liquid hourly space velocity of 32 hr.⁻¹,and a recycle gas to hydrocarbon mole ratio of 4:1. After a line-outperiod, a 20 hour test shows an average conversion of about 12%, and aselectivity for normal tetradecene of about 90%.

EXAMPLE IV

The catalyst contains, on an elemental basis, 0.3 wt. % platinum, 1.0wt. % cobalt, 0.25 wt. % zinc, and 0.6 wt. % lithium, with combinedchloride being less than 0.2 wt. %. The pertinent atomic ratios are: (1)Zn/Pt of 2.5:1, (2) Co/Pt of 11:1, and (3) Li/Pt of 56:1. The feedstream is substantially pure cyclohexane. The conditions utilized are atemperature of 900° F., a pressure of 100 psig., a liquid hourly spacevelocity of 3.0 hr.⁻¹, and a recycle gas to hydrocarbon mole ratio of4:1. After a line-out period, a 20 hour test is performed with almostquantitative conversion of cyclohexane to benzene and hydrogen.

EXAMPLE V

The catalyst contains, on an elemental basis, 0.2 wt. % platinum, 0.5wt. % cobalt, 0.25 wt. % zinc, 1.5 wt. % potassium, and less than 0.2wt. % combined chloride. The governing atomic ratios are: (1) Zn/Pt of3.7:1, (2) Co/Pt of 8.3:1 and (3) K/PT of 37:1. The feed stream iscommercial grade ethylbenzene. The conditions utilized are a pressure of15 psig., a liquid hourly space velocity of 32 hr.⁻¹, a temperature of1010° F., and a recycle gas to hydrocarbon mole ratio of 3:1. During a20 hour test period, 85% or more of equilibrium conversion of theethylbenzene is observed. The selectivity for styrene is about 90%.

It is intended to cover by the following claims, all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrogenation art.

I claim as my invention:
 1. A nonacidic catalytic composite comprising aporous carrier material containing, on an elemental basis, about 0.01 toabout 2 wt. % platinum group metal, about 0.05 to about 5 wt. % cobalt,about 0.1 to about 5 wt. % alkali metal or alkaline earth metal, andabout 0.01 to about 5 wt. % zinc, wherein the platinum group,catalytically available cobalt, zinc and alkali or alkaline earthcomponents are uniformly dispersed throughout the porous carriermaterial; wherein substantially all of the platinum group conponent ispresent in the elemental metallic state; wherein substantially all ofthe catalytically available cobalt component is present in the elementalmetallic state or in a state which is reducible to the elementalmetallic state under hydrocarbon dehydrogenation conditions or in amixture of these states; and wherein substantially all of the alkali oralkaline earth component is present in a positive oxidation state.
 2. Anonacidic catalytic composite as defined in claim 1 wherein the porouscarrier material is a refractory inorganic oxide.
 3. A nonacidiccatalytic composite as defined in claim 2 wherein the refractoryinorganic oxide is alumina.
 4. A nonacidic catalytic composite asdefined in claim 1 wherein the platinum group component is platinum. 5.A nonacidic catalytic composite as defined in claim 1 wherein theplatinum group component is iridium.
 6. A nonacidic catalytic compositeas defined in claim 1 wherein the platinum group component is rhodium.7. A nonacidic catalytic composite as defined in claim 1 wherein theplatinum group component is palladium.
 8. A nonacidic catalyticcomposite as defined in claim 1 wherein the alkali component ispotassium oxide.
 9. A nonacidic catalytic composite as defined in claim1 wherein the alkali component is lithium oxide.
 10. A nonacidiccatalytic composite as defined in claim 1 wherein the catalyticcomposite is in a sulfur-free state.
 11. A nonacidic catalytic compositeas defined in claim 1 wherein the composite contains, on an elementalbasis, about 0.05 to about 1 wt. % platinum group metal, about 0.1 toabout 2.5 wt. % cobalt, about 0.05 to about 1 wt. % zinc and about 0.25to about 3.5 wt. % alkali metal or alkaline earth metal.
 12. A nonacidiccatalytic composite as defined in claim 1 wherein the metals contentthereof is adjusted so that the atomic ratio of zinc to platinum groupmetal is about 0.1:1 to about 10:1, the atomic ratio of alkali metal oralkaline earth metal to platinum group metal is about 5:1 to about 100:1and the atomic ratio of cobalt to platinum group metal is about 0.1:1 to66:1.
 13. A nonacidic catalytic composite as defined in claim 1 whereinsubstantially all of the zinc component is present in the catalyticcomposite in a positive oxidation state.